In recent years, disk storage apparatuses have had significantly increased recording densities. Hard disk drives (HDDs) are known to represent the disk storage apparatuses. To allow high density recording to be achieved in an HDD, a magnetic head needs to be located as close to a surface of a magnetic disk (magnetic disk medium) as possible to such a degree that the magnetic head does not contact with the magnetic disk. A distance (spacing) between the magnetic head (hereinafter referred to as the head) and the magnetic disk (hereinafter referred to as the disk) is referred to as a head flying height.
For adjustment of the head flying height, a heater element is provided in the head. When supplied with power (heater power), the heater element generates heat and thus thermally deforms (expands) the head. The thermal deformation causes the head to be projected toward the surface of the disk and thus reduces the head flying height.
A phenomenon known as touchdown (more specifically, touchdown of the head) is utilized to determine the value of heater power needed to set the head flying height to a target value (hereinafter referred to as the operational heater power value). The touchdown refers to a phenomenon in which the head comes into contact with the disk. Here, it is assumed that the heater power increases step by step. In this case, the projection amount of the head gradually increases and eventually causes touchdown. A head disk interference sensor has been used to detect the touchdown.
The operational heater power value is determined based on a value of heater power provided when the touchdown is detected (hereinafter referred to as touchdown heater power). Thus, the touchdown needs to be sensitively and accurately detected in order to allow the head flying height to be accurately set to the target value.